A device which requires a user's manipulation should provide a UI for manipulating. The UI should be provided through a display or a touch screen, which is a factor in the increase of a manufacturing cost of the device.
However, in the case of a device which performs a relatively simple function, or a device which is not manipulated by a user very often, the increase in the manufacturing cost due to the above factor is irrational.
In addition, in order to change the UI of the device or add a new UI, the device itself should be changed. This leads to many works to the extent that a new device is developed.